An Efficient Hole Transporting Polymer for Quantum Dot Light-Emitting Diodes

Ideal hole transporting polymers used in quantum dot (QD) light-emitting diodes (QLEDs) should possess the features such as high conductivities and stabilized highest occupied molecular orbitals (HOMOs). Herein, an efficient polymer (named CNPr-TFB) is achieved by rationally adding a relatively weak electron-withdrawing group (2-cyanopropan-2-yl, CNPr) on a TFB like hole transporting polymer. CNPr-TFB exhibits a superior hole conductivity and much more stabilized HOMO in comparison with TFB. Therefore, much more holes are delivered into the QD emissive layers and a balanced recombination of electron and hole in the QLEDs is achieved. The external quantum efficiencies of the red, green, blue, and white QLEDs made by CNPr-TFB as the hole transporting layer (HTL) are 20.7%, 16.6%, 11.3%, and 15.0%, respectively, which are increased by 1.4–2.3 times in comparison with those of devices based on the commonly used TFB HTL. Meanwhile, the CNPr-TFB-based QLEDs also exhibit longer operation lifetimes than those of devices using the TFB HTL. These results confirm that CNPr-TFB with the features of high conductivity and stabilized HOMO can be an excellent HTL material for the QLED applications.